[.Net][Feature Request]: Eanble step-by-step execution for two agent chat API.

[LittleLittleCloud]

Is your feature request related to a problem? Please describe.

Similar to how GroupChatExtension.SendAsync returns an IAsyncEnumerable iterator, the AgentExtension.SendAsync(this IAgent agent, IAgent receiver, IEnumerable<IMessage> chatHistory, int maxRound = 10, CancellationToken ct = default(CancellationToken)) should also return an IAsyncEnuemrable so the conversation can be driven step by step.

Describe the solution you'd like

Return IAsyncEnumerabe in AgentExtension.SendAsync(this IAgent agent, IAgent receiver, IEnumerable<IMessage> chatHistory, int maxRound = 10, CancellationToken ct = default(CancellationToken))

Before

var chatHistory = new List<IMessage>()
{
   new TextMessage("Hey teacher, please create math question for me."),
};

var maxRound = 10;
while(true && maxRound > 0)
{
    IEnumerable<IMessage> conversation = await student.SendAsync(
            receiver: teacher,
            chatHistory: chatHistory,
            maxRound: 1);
    chatHistory = conversation;
    maxRound --;
}

After

var chatHistory = new List<IMessage>()
{
   new TextMessage("Hey teacher, please create math question for me."),
};

await foreach(var msg in student.SendAsync(receiver: teacher, chatHistory: chatHistory, maxRound: 10)
{
    // do something with msg. e.g. update chatHistory
    chatHistory.Add(msg)
}

API break change

this issue deprecates the following APIs. It's recommended to use GroupChatExtension.SendAsync instead

• AgentExtension.SendMessageToGroupAsync(IGroupChat, string, IEnumerable<IMessage>, int)
• AgentExtension.SendMessageToGroupAsync(IGroupChat, IEnumerable<IMessage>, int)

This issue also changes the return type of AgentExtension.SendAsync from Task<IEnumerable<IMessage>> to IAsyncEnumerable<IMessage>. You can use ToArrayAsync or something similar to convert IAsyncEnumerable to IEnumerable if you don't want to iterate over messages using await foreach

Additional context

See also #3214 on how groupchat.sendasync implement step-by-step execution by returning IAsyncEnumerable
No response